Aluminum brightener composition



United States Patent 3,326,803 ALUMINUM BRIGHTENER COMPOSITION Daniel R. Kelly, Southgate, and Lowell R. McCoy, Trenton, Mich., assignors to Wyandotte Chemicals Corporation, Wyandotte, Mich., a corporation ofMichigan No Drawing. Filed Apr. 27, 1964, Ser. No. 362,972 5 Claims. (Cl, 25279.4)

This invention relates to Ways and means for brightening aluminum surfaces of articles such as the Wings of aircraft. More particularly, it relates to aluminum brightener compositions based on methylcellulose as a thickener.

In the manufacture and use of articles having aluminum surfaces (including aluminum alloy surfaces), such as those found, for example, on aircraft, such surfaces become discolored, tarnished and covered with corrosion and oxidation products. For at least aesthetic reasons, it is desirable in many cases to remove such tarnish and corrosion products and discoloration, and otherwise brighten the surface of the aluminum article. A less obvious reason for removing such products of corrosion and oxidation resides in the fact that frequently cleaned aluminum surfaces tend to last longer than infrequently cleaned aluminum surfaces, or, to state it another way, in the fact that corrosion tends to beget corrosion. Consequently, the removal of corrosion products from aluminum articles upon completion of manufacturing operations has become a stranded finishing step and the frequent removal of corrosion products from aluminum articles in use has become a standard maintenance procedure, particularly in the aircraft industry.

In many instances, the removal of corrosion products and the like from aluminum and aluminum alloy surfaces can be accomplished merely by immersing the article into a' bath of an aqueous solution of a mineral acid and wetting agents, and, when the desired degree of brightening has occurred, by removing the article from the bath, rinsing and then drying. In the case of aircraft, however, it is unwieldy and impractical to dip or immerse the same into baths. Accordingly, it is customary in the aircraft industry to brush or spray the brightener solution on the aluminum surfaces to be brightened and, when the desired degree of brightening has occurred, to rinse the solution from the brightened surface. To prevent run-off and subsequent streaking of vertically disposed surfaces, the brightener solution under these conditions usually comprises a thickening agent, such as methylcellulose, in sufiicient concentration to make the solution sufiiciently viscous (about 80 to about 200 centipoises at 25 C.) and uniformly adherent to thesurface to be brightened.

However, such solutions (particularly those containing methylcellulose as the thickening agent) as have been developed by the art suffer from a major deficiency. They cannot be mass-produced in large quantities and shipped long distances to various points of use nor can they be stored for much more than 1 month for the reason that, as heretofore formulated, the. solutions rapidly lose viscosity. This loss in viscosity can be compensated for by initially formulating the solution with a sufiiciently higher concentration of thickening agent so that, even though degradation takes place, the solution will have the desired viscosity at a predetermined time of use. However, the raw material cost of such a solution is sufiiciently great as to discourage formulators at long distances from the point of use from supplying these solutions at reasonable prices to users. Moreover, because the storage life of such solutions is limited, users are not able to purchase such solutions in large quantities. Consequently, it has been customary to prepare the solution only in such quantities as will be used immediately and to do so at or near the place of use.

3,326,803 Patented June 20, 1967 Another deficiency of the prior art aluminum brighteners resides in the fact that they are in aqueous solution form. Elimination of water from the composition until the time of use would result in savings in shipping and handling costs. Elimination of the water does not, however, solve the problem of excessive loss in viscosity nor does it eliminate the liquid form of the brightener since the strong acids which make up the prior art compositions are liquid at the usual temperature of shipping and storage. Further, mere substitution of the strong, liquid acids by water-soluble, solid acids of equal strength or by solid, hydrolyzable acid salts that will produce acids of equal strength in aqueous solution does not prevent excessive degradation of the methylcellulose in the solid formulation and resultant low viscosity of the aqueous solution prepared at the time and place of use.

In US. Patent 2,942,956 an aluminum brightener composition employing methylcellulose is disclosed which, regardless of its age, gives upon addition of water an aluminum brightener solution with a viscosity within the desired range (about 80 to about 200 centipoises at 25 C.). This composition consists essentially of a finely divided mixture of about 10 to about 25 weight percent of a solid, hydrolyzable acid fluoride salt selected from the group consisting of alkali metal bifluorides, ammonium bifluoride and sodium silicofiuoride and mixtures thereof; about 20 to about 50 weight percent of a solid, watersoluble organic acid with an ionization constant in the range of about l 10 to about 2 10 about 15 to about 30 weight percent of a water-soluble methylcellulose of a viscosity type of about 400 to about 4,000 centipoises; and about 10 to about 30 weight percent of a water-soluble, acid-stable wetting agent. 4

While this composition produces the stated results and serves as a good cleaning composition for aluminum, it is limited to the use of an organic acid with an ionization constant in the range of about l 10 to about 2X10 and Example 5 of the patent demonstrates that an acid, i.e. sulfamic acid having an ionization constant of 1.01 1() is not at all stable in storage as compared to the formulations with ionization constants within the claimed range. While acids within the range make suitable cleaning compounds for aluminum, it is desirable to be able to use stronger acids, i.e., acids with an ionization constant greater than 2X10 since such acids have superior cleaning efficiency to those within the range and elfect the cleaning much more rapidly.

Accordingly, it is a purpose of this invention to provide the art with a dry, aluminum brightener composition comprising methylcellulose which, regardless of its age, will give upon addition of water an aluminum brightener solution with a viscosity within the desired range (about 80 to about 200 centipoises at 25 C.) which can readily be dissolved in water, and which is superior to the composition of Patent 2,942,956 in cleaning efficiency and in the rapidity of cleaning.

I In accordance with this invention, it has been discovered that oxalic acid, an acid having a first hydrogen ionization constant of 5.90 10 when substituted for the organic acid of the composition of Patent 2,942,956, gives superior cleaning efficiency and cleans much more rapidly than the composition of said patent. While such a substitution ordinarily results ina composition which is not at all stable in storage as compared to a formulation employing the acids set forth in the patent, the addition of urea in an amount from about 10 to 30 weight percent based on the total weight of the dry ingredients produces a cleaning solution with good storage stability and superior cleaning properties.

More specifically, this inventioncomprises a dry, aluminum brightener composition consisting essentially of a finely divided mixture of about 5 to about 25 weight percent of a solid, hydrolyzable acid fluoride salt selected from the group consisting of alkali metal bifluorides, ammonium bifluoride, sodium silicofluoride and mixtures thereof; about to about 30 weight percent of oxalic acid, about to about 30 weight percent of a watersoluble methylcellulose of a viscosity type of about 400 to 4,000 centipoises; about 2 to about 30 weight percent of a water-soluble, acid-stable wetting agent and about 10 to about 30 weight percent of urea.

The function of the acid fluoride salt is to provide hydrofluoric acid under conditions of use. Representative acid fluoride salts are ammonium acid fluoride, sodium acid fluoride, potassium acid fluoride and the like. Alkali metal, as used herein, refers to the monovalent elements of the first group of the periodic system, such as lithium, sodium, potassium, rubidium and cesium. Although alkali metal silicofluorides give good results when employed in the compositions of the invention, the aforementioned acid fluorides are more effective on heavily oxidized aluminum surfaces.

The concentration limits of the hydrolyzable acid salt are determined primarily by practical considerations. Too low a concentration results under use conditions in a brightening rate too slow for commercial acceptance. Too high a concentration and under use conditions the resultant rate of attack on aluminum becomes intolerable and, if the organic acid concentration is low enough, a white stain will be deposited on the metallic surface.

The oxalic acid functions under use conditions, both as sequestering agent and as an acidifying agent for the release of hydrogen fluoride by the acid fluoride salt.

The range of concentration of the oxalic acid in the dry composition is dependent on the brightening action. A concentration less than the minimum limit results in a brightening rate too low to be acceptable, a brightening action that is rapidly exhausted and white staining of the aluminum surface at higher concentrations of the acid fluoride salt. A concentration greater than the maximum limit will not produce any adverse effect; however, it is a practical limit based on the economics of the composition.

The methylcellulose under use conditions functions as a thickener or viscosity agent. It is well known in the art.

' Moreover, processes for producing methylcellulose are well known in the art. Methylcellulose is produced and sold according to viscosity type (which is a function of the methoxy content) and degree of purity. In general, technical grade to chemically pure methylcellulose can be used in the practice of this invention. The methylcellulose can be used as such or in the more common, hydroxypropyl modified, form. However, regardless of the degree of purity and the chemical form the methylcellulose used in the practice of this invention will usually be of a vis-' cosity type such that a 2 percent by weight aqueous solution thereof at C. will give an absolute viscosity in the range of about 400 to about 4,000 centipoises. A viscosity type below about 400 centipoises results in the minimum proportion of methylcellulose in the compositions of this invention being too large to be practicalJThe upper limit' on the viscosity type is dictated only by the fact larger.

viscosity types are not at present available in commercial quantities.

The range of concentration of methylcellulose in the composition is determined solely by the desired range of viscosities under use conditions, which range is from about 80 to about 200 centipoises at C. Since there is no substantial degradation of the methylcellulose in the presence of the other components of the compositions of this invention, no excess methylcellulose is involved in this range of concentration.

The water-soluble, acid-stable wetting agent component of the brightener composition aids in the penetration of the tarnish, etc. by the liberated hydrofluoric acid, as well as a more uniform cleaning action. It also functions to give a fine, stable foam when the composition under use conditions is rinsed from the brightened surfaces. Exemplary of nonionic wetting agents which can be used are (1) alkylarylpolyethers, such as the oxyethyl-ated adducts of nonyl phenol having an oxyethylene content in the range of about to about 85 weight percent of the total molecule and the oxyethylated adducts of tertiary octyl phenol having an oxyethylene content in the range of about 65 to about 75 percent by weight of the molecule, and (2) the polyoxyethylene-polyoxypropylene-polyoxyethylene (EPE) block polymer type of nonionics (see U.S. Patent No. 2,674,6*19Lundsted) which are marketed by Wyandotte Chemicals Corporation under the trade mark Pluronic, wherein the molecular weight of the polyoxypropylene base is in a range from 800 to about 2,500 and the oxyethylene content is from about 30 to about '80 weight percent of the total molecule, which wetting agents are well known in the art. Examples of acid-stable anionic wetting agents-which can be employed in the compositions of the invention include (1) the wellknown alkaryl-sulfonates such as sodium alkylbenzene sulfonate wherein the alkyl group has from about 10 to 18 carbon atoms and (2) the alkylsulfonates such as sodium laurlysulfate.

To minimize dust formation during handling of the solid compositions of this invention, a. small amount of liquid should be present in the composition.- This can be accomplished by using up to 10 weight percent of a liquid nonionic wetting agent in the composition. Beyond 10 Weight percent other handling problems, such as caking, are encountered, wherefore, in the solid compositions of this invention, which have a nonionic wetting agent concentration in excess of 10 weight percent, the excess should preferably be a solid nonionic wetting agent. Anv

such an EPE polyol is that marketed under the trademark Pluronic as F 68, in which the molecular weight of the polyoxypropylene base is in a range from about 1,500 to about 1,800 and the polyoxyethylene content is about 80 weight percent of the total molecule.

To prepare an aluminum brightener solution with the desired viscosity and brightening rate, the dry composition is mixed with suflicient Water to produce a solution in which the proportion of composition is from about 2.8 to about 9.5 weight percent and the proportion of water is from about 97.2 to about 90.5 weight percent and the mixing is continued until all of the solid composition has gone into solution.

To facilitate rapid dispersion and hydration of the methylcellulose component of the composition, the water used in making up the solution should be warm to hot. On the other hand, warm to hot water may not always be readily available or practical. Consequently, the solid composition may contain a dispersing agent. Although urea aids in the dispersing of the methylcellulose thickener, more rapid, uniform dispersion may be obtained by incorporating about 10 to 30 weight percent of an inorganic salt, such as ammonium sulfate, into the composition.

To use the aluminum brightener solutions of this invention, the solutions in the desired range of viscosity are merely brushed or sprayed on the surface to be brightened. The viscous solution remains in place and will eventually dry in place unless removed. About 30 seconds after applying the brightener solution, brightening action as evidenced by gas formation can be observed. After about 5 to 20 minutes, depending upon the condition of the oxidized aluminum surface, the brightening composi-- Examples 1-6 Examples of compositions suitable for use in aqueous solutions in accordance with the concepts of this invention are illustrated by Examples 1, 4 and 5 in the Table I below. The remaining examples in the table are for purposes of comparison of storage stabilities in terms of the viscosity properties of 6 percent by weight aqueous solutions of the compositions of the examples. More specifically, the examples of Table I below illustrate the storage stability of three typical compositions of this invention employing varying amounts of urea and ammonium sulfate (Examples 1, 4 and 5) as compared to the storage stability of a composition containing neither urea nor oxalic acid (Example 6); a composition employing oxalic acid but wherein no urea is employed (Example 3) and a composition wherein no surfactant is employed (Example 2 The aluminum brightener solutions, which were prepared for testing of the viscosity properties, were prepared by mixing 6 parts by Weight of the specified composition with 94 parts by weight of water. The viscosity was measured with a Brookfield Viscometer employing a No. 2 spindle at 30 r.p.m.

TABLE I Weight, Percent Components Ammonium Bifluoride 9. 9. 0 9. 0 9. 0 9. 0 9. 0 Ammonium Sulfate 19.0 26.0 39.0 29.0 9.0 64.0 Urea 20.0 20. 0 10. 0 30.0 Methylcellulose (Viscosity type ,000 cps.) 20.0 20.0 20.0 20.0 20.0 20.0 Igepal (IO-71 3.5 3.5 3.5 3.5 3.5 PhosphateEsterSurfaceA ve Agent 3. 3. 5 3.5 3.5 3 5 Oxalic Acid 25.0 25.0 25.0 25.0 25.0 Viscoshity Properties in cps. at

5 Days Storage:

Room Temp 255 250 105 270 220 355 14 155 115 30 75 135 240 The component identified as Igepal CO-710 is an oxyethylated adduct of nonylphenol which has an oxyethylene content of about 68 weight percent of the total molecule.

Example 3 illustrates that with a composition containing oxalic acid and all the other ingredients of the composition of this invention except urea, the viscosity of the aqueous solution after only 5 days storage at room temperature is substantially less than for the oxalic acid solutions containing urea and the aqueous solution of the composition of Example 6, Which latter composition contains all the ingredients of this invention except oxalic acid and urea.

From Examples 1, 2, 4 and 5, it can be seen that the compositions containing both oxalic acid and urea, even Where a surface active agent is not present, are characterized by a high degree of storage stability, thus demonstrating the superior stability obtained by incorporating urea in the compositions containing oxalic acid.

Example 7 This example illustrates the brightening of a tarnished aluminum surface with a composition of this invention.

A viscous liquid consisting of 6 parts by weight of the composition of Example 1 above and 94 parts by weight of water is prepared and then applied to a panel of an aluminum alloy (2024-T3 Alclad) which is disposed in a vertical position. After about 30 seconds the action of the brightener can be seen by the gassing that occurs at the surface of the aluminum alloy. Five minutes after placing the brightener composition on the panel, the composition is washed off from the panel under a stream of Water is prepared and then applied to a panel of an bright and free from streak marks and evidence of white deposits or corrosive pitting.

Examples 8-10 Additional examples of compositions suitable for use in aqueous solutions in accordance with the concepts of this invention are illustrated by Examples 8-10 in Table II.

The alkylaryl polyether alcohol, identified in the foregoing compositions as Triton X-100, is the oxyethylated adduct of tertiary octyl phenol having an oxyethylene content such that a 1 weight percent aqueous solution has a cloud point of 149 F. The EPE nonionic surface active agent, identified in the foregoing compositions as Pluronic L64, is a polyoxyethylene-polyoxypropylene-polyoxyethylene block polymer type of nonionic (see US. Patent No. 2,674,619-Lundsted) marketed by the Wyandotte Chemicals Corporation under the trademark Pluronic L64 wherein the molecular weight of the polyoxypropylene base is in the range of about 1,500 to 1,800 and the ethylene oxide content of the molecule is about 40 weight percent.

It is to be understood that various changes and modifications may be made in the foregoing without departing from the spirit of the invention and scope of the appended claims.

Also, the term consisting essentially of as used in the definition of ingredients present in the composition or compositions claimed is intended to exclude the preseence of significant amounts of other materials in such proportions as to interfere substantially with the properties and characteristics possessed by the compositions set forth while permitting the presence of other materials in such proportions as not substanially to affect adversely said properties and characteristics.

What is claimed is:

1. A finely divided composition suitable for use in aqueous solution at a concentration of about 2.8 to about 9.5 weight percent to brighten aluminum surfaces which consists essentially of about 5 to about 25 weight percent of a hydrolyzable acid fluoride salt selected from the group consisting of alkali metal bifiuorides, ammonium bifluoride, sodium silicofiuoride and mixtures thereof; about 10 to about 30 weight percent of oxalic acid; about 15 to about 30 weight percent of water-soluble methylcellulose of a viscosity type of about 400 to about 4,000 centipoises; about 2 to about 30 weight percent watersoluble, acid-stable wetting agent selected from the group consisting of anionic and nonionic wetting agents and about 10 to about 30 weight percent of urea.

2. A composition according to claim 1 including about 10 to 30 Weight percent of ammonium sulfate.

3. A composition suitable for use in aqueous solution at a concentration of about 5 parts by weight per parts by weight of water, which consists essentially of about 9.0 percent by weight of ammonium bifluoride;

about 25.0 percent by weight of oxalic acid; about 20 percent by Weight of methylcellulose of viscosity type of about 4,000 centipoises; about 7.0 percent by weight of water-soluble, acid-stable wetting agents selected from the group consisting of anionic and nonionic wetting agents; about 19 percent by weight of ammonium sulfate and about 20.0 percent by weight of urea.

4. An aluminum brightener composition consisting essentially of about 97.2 to about 90.5 weight percent of water and in solution about 2.8 to about 9.5 weight percent of a composition consisting essentially of about to about 25 weight percent of a hydrolyzable acid fluoride salt selected from the group consisting of alkali metal bifluorides, ammonium bifiuoride, sodium silicofluoride and mixtures thereof; about 10 to about 30 weight percent of oxalic acid; about to about 30 weight percent of a methyl-cellulose of a viscosity type of about 400 to about 4,000 centipoises; about 2 to about 30 weight percent water-soluble, acid-stablewetting agent-selected from the group consisting of anionic and nonionic wetting agents and about 10 to about 30 weight percent of urea, said liquid having a viscosity in the range of about 80 to about 200 centipoises at 25 C.

5. A method for brightening a tarnished aluminum surface which comprises (1) applying to said surface a viscous liquid consisting essentially of about 97.2 to about 90.5 weight percent of water and in solution about 2.8

to about 9.5 weight percent of a composition consisting essentially of about 5 to about 25 weight percent of a hydr-olyzable acid fluoride salt selected from the group consisting of alkali metal bifluorides, ammonium bifluoride, sodium silicofluoride and mixtures thereof; about 10 to about weight percent of oxalic acid; about 15 to about 30 weight percent of a methyl-cellulose of a viscosity type of about 400 to about 4,000 centipoises; about 2 to about 30 weight percent Water-soluble, acid-stable wetting agent selected from the group consisting of anionic and nonionic wetting agents and about 10 to about 30 weight percent of urea, said liquid having a viscosity in the range of about to about 200 centipoises at 25 C.; and (2) rinsing said solution from said surface when the tarnish on said surface has been removed therefrom.

References Cited UNITED STATES PATENTS 1,554,483 9/1925 Bailey et al 134-28 2,942,956 6/1960 Kelly 25279.4 3,061,494 10/1962 Snyder et a1 25279.3

LEON D. ROSDOL, Primary Examiner.

DONALD E. CZAJA, Examiner.

W. E. SCHULZ. Assistant Examiner. 

1. A FINELY DIVIDED COMPOSITION SUITABLE FOR USE IN AQUEOUS SOLUTION AT A CONCENTRATION OF ABOUT 2.8 TO ABOUT 9.5 WEIGHT PERCENT TO BRIGHTEN ALUMINUM SURFACES WHICH CONSISTS ESSENTIALLY OF ABOUT 5 TO ABOUT 25 WEIGHT PERCENT OF A HYDROLYZABLE ACID FLUORIDE SALT SELECTED FROM THE GROUP CONSISTING OF ALKALI METAL BIFLUORIDES, AMMONIUM BIFLUORIDE, SODIUM SILICOFLUORIDE AND MIXTURES THEREOF; ABOUT 10 TO ABOUT 30 WEIGHT PERCENT OF OXALIC ACID; ABOUT 15 TO ABOUT 30 WEIGHT PERCENT OF WATER-SOLUBLE METHYLCELLULOSE OF A VISCOSITY TYPE OF ABOUT 400 TO ABOUT 4,000 CENTIPOISES; ABOUT 2 TO ABOUT 30 WEIGHT PERCENT WATERSOLUBLE, ACID-STABLE WETTING AGENT SELECTED FROM THE GROUP CONSISTING OF ANIONIC AND NONIONIC WETTING AGENTS AND ABOUT 10 TO ABOUT 30 WEIGHT PERCENT OF UREA. 